Virtualization involves creation of an abstracted system on a hardware platform. A hypervisor creates one or more virtual machines on a computer system and manages resource, memory, and device allocation for the virtual machines. The hypervisor may be installed directly on the hardware or may be installed on a host operating system. Each virtual machine has abstracted components such as a processor, memory, and I/O devices, as well as an installed guest operating system.
Virtual machines often perform parallel tasks and are managed with regard to the tasks. A virtual machine may fail due to hardware failure, firmware failure, power loss, or other casualty that interrupts operation of the virtualized system. High availability is the concept of maintaining service of virtual components in the event of such a failure.